Re: [PATCH 3/3] smp/ipi:Remove check around csd lock in handler for smp_call_function variants

[Wang YanQing <udknight@gmail.com>]

On Fri, Jul 05, 2013 at 09:57:21PM +0530, Preeti U Murthy wrote:
> call_single_data is always locked by all callers of
> arch_send_call_function_single_ipi() or
> arch_send_call_function_ipi_mask() which results in execution of
> generic_call_function_interrupt() handler.
> 
> Hence remove the check for lock on csd in generic_call_function_interrupt()
> handler, before unlocking it.

I can't find where is the generic_call_function_interrupt :)

> Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
> Cc: srivatsa.bhat@linux.vnet.ibm.com
> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Rusty Russell <rusty@rustcorp.com.au
> ---
> 
>  kernel/smp.c |   14 +-------------
>  1 file changed, 1 insertion(+), 13 deletions(-)
> 
> diff --git a/kernel/smp.c b/kernel/smp.c
> index b6981ae..d37581a 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -181,25 +181,13 @@ void generic_smp_call_function_single_interrupt(void)
>  
>  	while (!list_empty(&list)) {
>  		struct call_single_data *csd;
> -		unsigned int csd_flags;
>  
>  		csd = list_entry(list.next, struct call_single_data, list);
>  		list_del(&csd->list);
>  
> -		/*
> -		 * 'csd' can be invalid after this call if flags == 0
> -		 * (when called through generic_exec_single()),
> -		 * so save them away before making the call:
> -		 */
> -		csd_flags = csd->flags;
> -

You haven't mention this change in the ChangeLog, don't do it.
I can't see any harm to remove csd_flags, but I hope others
check it again.

>  		csd->func(csd->info);
>  
> -		/*
> -		 * Unlocked CSDs are valid through generic_exec_single():
> -		 */
> -		if (csd_flags & CSD_FLAG_LOCK)
> -			csd_unlock(csd);
> +		csd_unlock(csd);

I don't like this change, I think check CSD_FLAG_LOCK 
to make sure we really need csd_unlock is good.

Just like you can't know who and how people will use the
API, so some robust check code is good.